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Absh-act-The capability of the 'Self-Training Interpretive and Retrieval System' has been extended so that the compounds selected as providing the best match in each data class to the unknown mass spectrum are examined by the computer for the presence of each of 179 common substructural fragments. Statistical methods were used to evaluate the selectivity for identification of each substructure by each data class using a reference file of 18 806 spectra of different compounds. In tests using at least 373 unknown spectra for each of the substructures, with criteria that gave a mean reliability of 98.1 %, the method averaged 49% recall, which corresponds to the identification of 2.55 substructures per unknown spectrum on average. Calculation of the substructure probability values for the unknown spectrum, as well as the normal 'Self-Training Interpretative and Retrieval System' match-factor results, requires 68 s on a laboratory computer. The method is also available to outside users on an international computer network.

true spectrum background and to determine the effectiveness of the steel shielding, the system was purged with air, the stopcocks were closed, and the experiment was repeated. No 197Hg gamma-rays were observed. CONCLUSIONAbsorption of energy during neutron irradiation of hydrocarbons may trigger a chemical reaction. It is believed this results in the formation of elemental mercury, which is then lost by diffusion as vapor. The amount of mercury that is made available for the diffusion loss as vapor is dependent on the chemical nature of the solvent, as observed in differences in the loss rate with different hydrocarbon stocks. The intensity of the flux is also a factor.If polyethylene vials are used for irradiation and counting, the samples should be counted within a few hours after the irradiation. However, this is often impractical such as in cases where the samples have a high 24Na activity. We, therefore, recommend the use of sealed quartz vials in the determination of mercury in a hydrocarbon matrix even if the irradiation time is only 1 hour or less and the neutron flux only 1012 n cm-2 sec-1.

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